FoamPyc Technique Determines Open Cell Volume in Foamed Materials
The FoamPyc option for the AccuPyc 1340 Density Analyzer lets you measure, calculate, and report the percentage of open cell volume in blocks of foamed or cellular plastic, glass, rubber, or metal.
These foamed materials have thin membranes or walls that separate internal cavities or cells. These cells can be open or interconnecting, closed or non-connecting, or a combination of open and closed. With the FoamPyc flashcard, you can determine the percentage of sample volume occupied by open cells, as well as closed cells.
A Focus on Accuracy
The FoamPyc program ensures accuracy by correcting for punctured cells caused by cutting the block of material to obtain a sample. The volume of the cells that were opened on the cut surfaces of the sample are computed and their volume deducted from the analysis results so as not to overstate the true open-cell volume of the original uncut material.
The program uses correction calculations that follow ASTM Standard D 6226. Procedure "A" factors in cell chord length for estimating cut cell volume. Procedure "B" performs a second analysis to correct for opened cells, except this time the same sample is subdivided
(re-cut) to expose twice the total surface area as before. Then, the second run is subtracted
from the first run using a correction calculation, V= 2(V + D) - (V + 2D), where V is the true open-cell volume and D is the cut cell volume. Procedure "C" performs an AccuPyc analysis on the cut sample as is, which works well with samples that have mostly open cells.
Procedure "D" permits the volume change of soft, closed cell foams to be measured by applying progressively larger amounts of isotropic gas pressure and computing the volume occupied by the foam. Procedure "E" evaluates the possibility of fracturing, which may occur when closed cell foam made of brittle material (having large, thin-walled cells) is exposed to pressure. This method applies first a small, controlled amount of pressure, and then performs a volume measurement. Next, a larger amount of pressure is applied. The sample is then returned to the first pressure and volume measurement is repeated.
Micromeritics announces the availability of a FoamPyc Sample Preparation Kit, Part No. 133/33009/00, to enhance your assessment of open pores in plastic foams. ASTM Test Method D-6226 describes the technique for extracting a sample of foam of specific dimensions then re-cutting it to double the amount of exposed surface, thereby deriving a correction for the pores opened in the initial cutting. The kit contains a knife, extra blades and a guide structure for both the first cutting of sample to dimensions and the re-cutting.